Purpose: To compare the infusion pressure shown by a vitrectomy device with the actual intraocular pressure (IOP) observed during pars plana vitrectomy. Furthermore, we evaluated the effects of variable parameters on the actual IOP during vitrectomy surgery. Materials and methods: Porcine eyes were obtained within 24 h of slaughter. Actual IOP was measured by a digital manometer during vitrectomy using the vented gas forced infusion (VGFI) system, as well as the gravity system. We analyzed the actual IOP according to the groups divided by remnant volume of infusion fluid: (500 ml; control group, 250, 125, and 50 ml). Finally, actual IOP was determined after changing variable parameters such as cutting rate, vacuum pressure, and the VGFI setting. Results: Settings for a VGFI system and pressure supplied by a gravity system significantly correlated with actual IOP (r = 0.99, p = 0.0001; r = 0.99, and p = 0.0001). Actual IOP declined with decreasing volume of infusion fluid. If the volume of infusion fluid was <125 ml, actual IOP decreased significantly compared with the control group and the difference in actual IOP reflected a significant difference in the VGFI setting of 30 mmHg. Cutting rate as well as VGFI setting and vacuum pressure affected actual IOP. Conclusions: Infusion pressure shown by the vitrectomy device was similar to actual IOP in porcine eyes. However, volume of infusion fluid and variable parameters could change the actual IOP during pars plana vitrectomy. Our results may help to optimize the ideal parameters such as infusion pressure, vacuum pressure, and cutting rate of vitrectomy systems used to treat vitreoretinal diseases.